The synaptic vesicle monoamine transporter (SVMT) transports monoamine neurotransmitters into synaptic vesicles, and recognizes amphetamines including MDMA ("ecstasy") as substrates. Amphetamine is a weak bases that may enter the vesicle via this transporter and/or by passive diffusion to elevate the Ph of the vesicle's acidic interior and precipitate release of stored neurotransmitter. In the current FY, a human CDNA clone which encodes the SVMT protein has been isolated and sequenced. The human protein of 514 amino acids shares 92% amino acid identity with a previously isolated rat homolog, but displays slight differences in consensus sites for glycosylation and phosphorylation. The human SVMT gene mapps to chromosome 10q25 using Southern blotting and fluorescent in situ hybridization approaches. Northern analysis reveals expression of 3 kb MRNA in human brainstem and 4.8 kb MRNA in hypothalamus. Substantial expression in human nigra compacta neurons and in apparent histaminergic hypothalamic neurons in rat was detected. COS cell hSVMT expression yielded nanomolar affinities for tetrabenazine and reserpine, micromolar affinities for haloperidol, GBR-12909, serotonin, mazindol, nomifensin and d-amphetamine, and millimolar affinities for dopamine, epinephrine, norepinephrine and histamine.